This invention relates to a system and method for the emergency operation of a static Scherbius device including, as indicated in FIG. 1, a wound-type induction motor 1, a converter 2 for converting the secondary a.c. power of the motor 1 into d.c. power, a d. c. reactor 3 for smoothing the d.c. output from the converter 2, and an inverter 5 for converting the d.c. power into a.c. power and regenerating it to the a.c. power source 4, which system and method are particularly useful for a short time voltage failure or a short time abnormal voltage drop of the power source.
In the above-described static Scherbius device, the rotating speed of the induction motor 1 can be controlled by varying the leading angle of the inverter 5, and the inverter 5 undergoes the commutating operation by the use of the power source a.c. voltage. For this reason, if any short-circuit trouble, grounding trouble, or change-over of power source system occurs on the power source side of the Scherbius device, a voltage drop in the range of 0 to 70% of the power source voltage, or an entire power failure, frequently results for a period ranging from serveral cycles to several minutes, and such a voltage drop or power failure can cause commutation failure in the inverter 5. The commutation failure in turn causes blowing out of the protecting fuse for the thyristors in the inverter 5, thus, not only making the Scherbius device inoperative, but also causing malfunction of the entire plant including the Scherbius device.